Application of the HEC-RAS Model in Flood Modeling on the Code River Segment in Sewon District, Bantul Regency, Indonesia

Abstract

Research on flood hazard and risk mapping has been widely conducted and is crucial for flood disaster management and mitigation. These studies often involve flood modeling using HEC-RAS, which has been applied to major rivers in the Special Region of Yogyakarta Province. This modeling analyses the area and depth of inundation using parameters such as flood hydrographs, Manning’s coefficient, and Digital Elevation Model (DEM) data. This study aims to compare the discharge simulated by the GAMA I Synthetic Unit Hydrograph (HSS GAMA I) model with observed discharges using loggers and to evaluate flood modeling with HEC-RAS in Sewon District, Bantul Regency. The results of flood modeling predictions using two different discharge inputs are not too different in terms of discharge and inundation area. Peak discharge values using HSS Gama I are determined as 29.70 m³/s, 52.11 m³/s, and 64.20 m³/s for 2, 5, and 10-year return periods respectively, while values obtained using loggers are 26.16 m³/s, 41.53 m³/s, and 49.56 m³/s. It can be concluded that discharge data from the HSS GAMA I method can still be considered relevant to be used as an alternative method if discharge data is not obtained from direct measurements. Geometry data obtained from the results of aerial photography that is regressed with terrestrial data is also important in this study because it can adjust the basic data and the latest data into one good geometry data. At least the data produced can represent the geometry of the modeled river as closely as possible to the conditions in the field and the results of this study can be a new reference for further research to be able to apply the model and adjust it to the character of each region, so that flood modeling using HEC-RAS becomes more innovative and adaptable to the modeled area.